Cancer arising from the cervix is the number one cancer in women in many countries. About 30% of cancers in women are due to cervical cancer with more than 100,000 new cases diagnosed every year, e.g., in India.
After a positive screening test for cervical cancer, colposcopic examination is routinely used as the second diagnostic step by gynecologists for identification of abnormal areas of the cervix. A colposcope is a low-power, stereoscopic, binocular field microscope with a powerful light source used for magnified visual examination of the uterine cervix to help in the diagnosis of cervical cancer.
A routine test for cervical cancer applied worldwide, and in which a colposcope is used, involves the reaction of tissue to the administration of acetic acid and iodine solution to the cervix.
A colposcope is used to identify visible clues suggestive of abnormal tissue. It functions as a lighted binocular microscope to magnify the view of the cervix, vagina, and vulvar surface. Low power (2× to 6×) may be used to obtain a general impression of the surface architecture. Medium (8× to 15×) and high (15× to 25×) powers are utilized to evaluate the vagina and cervix. The higher powers are often necessary to identify certain vascular patterns that may indicate the presence of more advanced precancerous or cancerous lesions. Various light filters are available to highlight different aspects of the surface of the cervix.
Acetic acid (usually 3-5%) is applied to the cervix by means of, e.g., cotton swabs, or spray.
Areas with a high risk of neoplasia, or cancer, will appear as varying degrees of whiteness, because acetowhiteness correlates with higher nuclear density. The term “acetowhiteness” is used in contradistinction to areas of hyperkeratosis or leukoplakia which appear white before the application of acetic acid. The transformation zone is a critical area on the cervix where many precancerous and cancerous lesions most often arise. The ability to see the transformation zone and the entire extent of any visualized lesion determines whether an adequate colposcopic examination is attainable.
Areas of the cervix which turn white after the application of acetic acid or have an abnormal vascular pattern are often considered for biopsy. Iodine solution is applied to the cervix to help highlight areas of abnormality, and distinguish metaplastic regions from suspicious lesions.
After a complete examination, the colposcopist determines the areas with the highest degree of visible abnormality and may obtain biopsies from these areas using a long biopsy instrument. Most doctors and patients consider anesthesia unnecessary. However, some colposcopists now recommend and use a topical anesthetic such as lidocaine or a cervical block to diminish patient discomfort, particularly if many biopsy samples are taken.
Extensive training is needed to correctly interpret a colposcope test according to the above protocol. In emerging markets like India and China lack of trained resources and expertise limit the usage of this effective diagnostic tool. The same situation applies for industrialized countries, where qualified medical personnel are in short supply.
Colposcopy diagnosis requires expertise and involves detection of specific image features for precise diagnosis of uterine cervix diseases. This makes automation in this area challenging. Of the several features considered to make a diagnosis one of the important features is the punctation marks present on the cervix region: they are a marker of abnormal vessels' architecture and their presence is significantly correlated to the existence of pre- and cancerous lesions of the cervix.